The ganglíosides of the chicken retina and optic tectum. The influence of light on their labelling after an injection of labelled precursors.

Cultures of retinas from 8-day-old embryonic chicken in the presence of (3)H -glucosamine showed that GD3 and GM3 are the gangliosides with highest labelling. From this age onward, and apparently responding to the appearance of the required enzymes, the labelling of GM1, GD1a and GT increases and at hatching day GD1a becomes the highest labelled ganglioside. The main site of synthesis of neuronal gangliosides was found in the neuronal perikarya, in a Golgi membrane enriched fraction. In this fraction the nascent gangliosides are protected from the neuraminidase attack. Experiments in the visual system of chicks indicated that the gangliosides synthesized in the soma of retinal ganglion cells are transported axonally to their endings in the contralateral optic tectum. After 3, 5 and 8 h of injection of N (3)H acetylmannosamine into one eye of the chick, the gangliosides in the contralateral optic tectum of animals exposed to 1000 lux were more labelled than in their controls in dark. The glycoproteins followed a pattern of labelling similar to that of gangliosides. Most of the difference in labelling appears in the same subcellular fraction in which normally is found the maximal deposition of gangliosides. The increase of labelling was not due to a greater turnover of gangliosides.